Currently, in 3GPP RAN LTE (Long Term Evolution) studies are being conducted for a RACH transmission method. The RACH refers to an uplink channel which a mobile station uses upon transferring from idle mode to a calling step and to transmit information required to establish a scheduled channel to the base station. The RACH cannot be scheduled by the base station, and so a mobile station takes the initiative in randomly selecting transmission resources (e.g. code pattern). If the transmission resources overlap between a plurality of users and their RACH's collide, the base station cannot receive these successfully, and the mobile stations have to retransmit the RACH's.
In LTE, including at least a signature, which is terminal identification information, into the RACH, is studied. Moreover, as the configuration of the signatures as in W-CDMA (Wideband-Code Division Multiple Access), to improve C/N by detecting different signatures at the same time and by spreading gain, studies are conducted for separating mobile station signature numbers using signature patterns (code patterns) of good correlation characteristics.
In a conventional RACH signature pattern, codes that have good autocorrelation characteristics and cross-correlation characteristics and have low PAPR (Peak to Average Power Ratio), are used in order to detect the signatures (terminal identification information) based on correlation characteristics calculated at the receiving side. As a code sequence having these features, the cyclic shift based CAZAC sequence shown in FIG. 1 is known (see non-Patent document 1). This is a code sequence obtained by cyclically shifting a, CAZAC sequence, so that it is possible to detect different signatures at the receiving side at the same time by associating signature numbers with cyclic shift values. Features of CAZAC (Constant Amplitude Zero Auto-Correlation) include good autocorrelation characteristics and zero correlation between codes shifting the same code. Moreover, these CAZAC codes show relatively low cross-correlation but are not completely orthogonal. Non-patent Document 1: 3GPP, R1-060046, NTT DoCoMo, “Orthogonal Pilot Channel Structure in E-UTRA Uplink”